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A new spectrometer for the coincidence study of (e,2e) single ionization, and e,(3-1)e or (e,3e) double ionization by electron impact is described. The system is based on two double toroidal analyzers for the ejected electrons and a cylindrical electrostatic analyzer for the scattered electrons. It allows angular and energy distributions of the ejected electrons to be measured over almost the totality of the collision plane, using dual two-dimensional position sensitive detectors. The design and operation of the spectrometer is described with a special emphasis on the imaging properties of the system. The performance (energy and angular resolutions,…) and the calibration of the spectrometer are discussed and sample results for (e,2e), e,(3-1)e and (e,3e) experiments on the rare gases are presented.

We describe new developments aimed to extend the capabilities and the sensitivity of the (e,2e)(e,3e) multicoincidence spectrometer at Orsay University [Duguet et al., Rev. Sci. Instrum. 69, 3524 (1998)]. The spectrometer has been improved by the addition of a third multiangle detection channel for the fast "scattered" electron. The present system is unique in that it is the only system which combines three toroidal analyzers all equipped with position sensitive detectors, thus allowing the triple coincidence detection of the three electrons present in the final state of an electron impact double ionization process. The setup allows measurement of the angular and energy distributions of the ejected electrons over almost the totality of the collision plane as well as that of the scattered electron over a large range of scattering angles in the forward direction. The resulting gain in sensitivity ( approximately 25) has rendered feasible a whole class of experiments which could not be otherwise envisaged. The setup is described with a special emphasis on the new toroidal analyzer, data acquisition hardware, and data analysis procedures. The performances are illustrated by selected results of (e,2e) and (e,3e) experiments on the rare gases.

Elastic and inelastic differential cross sections (DCS) of high energy electrons (25 keV) scattered by neon and argon have been separately measured by totally independent methods. The effects of electronic correlations on the DCS and on the radial distribution functions D(R) and P(R) are deduced from experiment by comparison with theoretical Hartree–Fock values. An estimate of the correlation energy is also given. In the case of neon, the differences, with respect to Hartree–Fock, of the various contributions to atomic potential energy Δ Vne, Δ VeeCoul, and ΔVeeexch are calculated from experiment and compared to theoretical results.

A new high‐energy spectrometer for the coincident detection of both outgoing electrons in an electron impact ionization, or (e, 2e), experiment is described. The absolute triple differential cross section can be measured with this instrument to a precision of 10%. Selected results on rare gases are presented, demonstrating the ability of the spectrometer to either probe the target structure in impulsive or binary (e,2e) experiments, or to test the scattering mechanism in nonimpulsive conditions, both for valence or inner shells.

High‐precision relative energy‐loss spectra of 25 keV electrons scattered from neon atoms are measured in the momentum transfer range 0.5 a.u.

From the measurement of high energy elastic and inelastic electron scattering by the NH3 molecule we find that molecular elastic scattering calculation agrees with experiment, but the independent atom model for molecular inelastic scattering does not reproduce the experiment, even when electron correlations are taken into account. This means that the inelastic scattering by molecules is strongly affected by the rearrangement of the charge densities during the bond formation.